Celestia coordinate system

[SergeiK]

Where can I find information about coordinate system used in Celestia ?
From the glossary I have found out the next:

"Universal Coordinate System
The default coordinate system used by Celestia is Ecliptic J2000:
The fundamental plane is the J2000 Earth ecliptic, and the preferred direction (x-axis) is the J2000 equinox."

But it is difficult for me to gain the understanding of
1) Where is the origin of that default coordinate system ?
2) If that system is "default" than there are some other coordinate systems used by Celestia -- where can I find information on them ?

[selden]

Where can I find information about coordinate system used in Celestia ?
From the glossary I have found out the next:

"Universal Coordinate System
The default coordinate system used by Celestia is Ecliptic J2000:
The fundamental plane is the J2000 Earth ecliptic, and the preferred direction (x-axis) is the J2000 equinox."

But it is difficult for me to gain the understanding of
1) Where is the origin of that default coordinate system ?

The Solar System's barycenter: the point around which the Sun and planets orbit.

2) If that system is "default" than there are some other coordinate systems used by Celestia -- where can I find information on them ?

There are several different ones that you can specify: ecliptic, equatorial, body centered, etc. They're described in the Celestia Wikibook, which is available at http://en.wikibooks.org/wiki/Celestia

[posfan12]

The x-axis in the J2000 coordinate system is parallel to Earth's equinox IIRC. Hope that helps.